Handy Holley Tuning Tip - Chevelle Tech
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post #1 of 13 (permalink) Old Jan 15th, 20, 7:09 PM Thread Starter
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Handy Holley Tuning Tip

We learned this little tip from Phil Freelander at FST Carburetors based on his decades of experience. There are six flats on a Holley carburetor float adjustment hex-head screw. If you raise or lower the float level adjustor by four flats (two-thirds of a turn), this is the equivalent of two jet sizes. For example, raising the float level four flats would be the same as changing from 78 to 80 jets. Lowering the float level will lean the air-fuel ratio.

This is based on the height of the fuel level in the float bowl. Increasing the float-height richens the mixture because it increases the pressure on the main jets located at the bottom of the column of fuel in the bowl. This is not a carved-in-stone rule, but changing the float level will certainly affect the overall air-fuel ratio and can be used for minor changes in overall jetting. It’s best not to alter the float level beyond this point in either direction — but if you need to make a change in a hurry, it will work.


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post #2 of 13 (permalink) Old Jan 15th, 20, 7:26 PM
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Re: Handy Holley Tuning Tip

yeah, this is right. I used to use this trick on my 69 Z/28 if I was go on any kind of a hiway drive. I used 1/2 turn down on the primary. I knew I wasn't going to be lead footing it so I didn't care about the secs. Helped to the tune of about 1.5MPG.
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post #3 of 13 (permalink) Old Jan 15th, 20, 7:44 PM
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Re: Handy Holley Tuning Tip

Read this same tip 1 day ago on Chevy Hardcore, along with some others. Take a look.

https://www.chevyhardcore.com/tech-s...nd-procedures/
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post #4 of 13 (permalink) Old Jan 15th, 20, 8:20 PM
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Re: Handy Holley Tuning Tip

Thanks, going to have to try it to see if I can better the 3 gallons / per mile I am currently getting.

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post #5 of 13 (permalink) Old Jan 18th, 20, 5:04 PM
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Re: Handy Holley Tuning Tip

I worked at Holley for over 5 years, and I never saw the need, nor sensible reasoning to vary the float levels to change jetting, only needed to....change the jetting.

To each, their own insanity, it seems.
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post #6 of 13 (permalink) Old Jan 18th, 20, 5:32 PM
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Re: Handy Holley Tuning Tip

I use this method now. Raising fuel level adds more volume which in turn adds more weight . Especially beneficial during high weather pressure by further increasing the super charge effect. I did not know about the 2 jet thing. I run my float levels at the top of the sight glass.


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post #7 of 13 (permalink) Old Jan 18th, 20, 7:50 PM
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Re: Handy Holley Tuning Tip

This cant be a precise science since the fuel level in the sight window is basically an eyeball estimation. And since most garage floors have a pitch to them, getting the fuel level in the center of the window is probably off a bit when you're initially adjusting the floats.

So, I might be two or three flats above or below before I even start messing with the adjustor.

Or am I thinking too much into this ?

I guess I'll just leave it centered in the window, the way Holley designed it.
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post #8 of 13 (permalink) Old Jan 18th, 20, 7:55 PM
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Re: Handy Holley Tuning Tip

My 3310 calls for the fuel level to be even with the bottom of the site screw hole.

Your just jealous because you can't hear the voices!

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post #9 of 13 (permalink) Old Jan 18th, 20, 8:27 PM
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Re: Handy Holley Tuning Tip

Obviously it doesn't matter where the fuel level was to start with .if you raise the fuel level over this arbitrary value or lower it you richen or lean the mixture it's just basic physics. Obviously you don't want to raise the fuel level enough to cause flooding. Raising or lowering Inlet fuel pressure accomplishes the same thing
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post #10 of 13 (permalink) Old Jan 18th, 20, 8:45 PM
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Re: Handy Holley Tuning Tip

Quote:
Originally Posted by Dave Ray View Post
I worked at Holley for over 5 years, and I never saw the need, nor sensible reasoning to vary the float levels to change jetting, only needed to....change the jetting.

To each, their own insanity, it seems.
Agreed..

It might be a quick hack to see if jetting should be changed.


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post #11 of 13 (permalink) Old Jan 18th, 20, 8:58 PM
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Re: Handy Holley Tuning Tip

The lesson here is not necessarily use float level changes to change afr but to know that it does effect it. Raising float levels richens the entire carb where changing jets idle intermediate etc only changes thier respective circuit. Changing float levels a few Flats is a good quick way make an afr change to see what the engine wants
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post #12 of 13 (permalink) Old Jan 20th, 20, 3:47 PM
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Re: Handy Holley Tuning Tip

Used as a tuning check tool, extremely marginal info/feedback input, done the right way in setting the correct fuel liquid level, absolutely essential to doing it right.

And, it isn't the fuel volume weight that is in play, but the change in the amount of fuel pulled in for the vacuum level pull. At the same vacuum, lower liquid level, harder vacuum pull, higher, easier fuel pull, but, that is what the jets, fixed air bleeds and air correctors are for. Plus, too high can lead to fuel dribble into jet passages, richness and just plain rotten engine running.

This is a lot like soe sizes for one set dimension foot, too big, problems, too small, problems, and PAIN.

As far as carb angle being effected by vehicle attitude, none of you guys ever hear of a carburetor wedge for a BOAT?
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post #13 of 13 (permalink) Old Jan 20th, 20, 4:17 PM Thread Starter
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As far as carb angle being effected by vehicle attitude, none of you guys ever hear of a carburetor wedge for a BOAT?

Pretty sure I remember wedge manifolds and or wedges for inboards of the 60’s ???
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